模拟大质量星风的宽带X射线吸收
Modeling broadband X-ray absorption of massive star winds
摘要：
我们提出了一种方法来计算从大质量恒星的冲击加热等离子体分布在整个部分光学厚的恒星风发射的X射线的净传输。我们发现传输的正式解决方案的精确积分，假设发射等离子体和吸收等离子体混合在一个恒定的质量比以上的一些最小半径，低于该半径假设是没有排放。该模型比与风底部日冕相关的平板吸收或假设所有观测到的X射线从光学深度单位半径以上发射而没有衰减的外逸层近似更现实。我们的模型在XSPEC中实现为一个预先计算的表，可以耦合到用户定义的表的波长相关的风不透明度。我们提供了一个默认的风不透明度模型，比常用的中性星际介质（ISM）制表更能代表真实的风不透明度。\textit{Chandra}光栅数据的初步建模表明，光谱亚型OB星的X射线硬度趋势在很大程度上可以理解为风吸收效应。
英文摘要：
We present a method for computing the net transmission of X-rays emitted by shock-heated plasma distributed throughout a partially optically thick stellar wind from a massive star. We find the transmission by an exact integration of the formal solution, assuming that the emitting plasma and absorbing plasma are mixed at a constant mass ratio above some minimum radius, below which there is assumed to be no emission. This model is more realistic than either the slab absorption associated with a corona at the base of the wind or the exospheric approximation that assumes that all observed X-rays are emitted without attenuation from above the radius of optical depth unity. Our model is implemented in XSPEC as a pre-calculated table that can be coupled to a user-defined table of the wavelength dependent wind opacity. We provide a default wind opacity model that is more representative of real wind opacities than the commonly used neutral interstellar medium (ISM) tabulation. Preliminary modeling of \textit{Chandra} grating data indicates that the X-ray hardness trend of OB stars with spectral subtype can largely be understood as a wind absorption effect.
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